Revision of Proximity Rules for Subsurface Transforming to Surface Flaws for Class 1 Ferritic Vessels

There is a rule in Acceptance Standards of Class 1 ferritic vessel in the ASME B&PV Code Section XI describing that allowable subsurface flaws near a component surface are transformed to allowable surface flaws. This is the flaw-to-surface proximity rule for the subsurface flaws. If the subsurface flaw is located closer to the component surface, the subsurface flaw not allowed close to the component surface but may be acceptable after transforming it to a surface flaw. This is a discontinuity of a subsurface flaw in the current Acceptance Standard for Class 1 ferritic vessels. Authors had developed a solution for the discontinuity and proposed the proximity rule at the last ASME PVP 2006 conference. After the discussion at the ASME Code Working Group on Flaw Evaluation, the proposed proximity rule was revised. This paper describes the revision of new flaw-to-surface proximity rule to minimizing the changes to the current allowable subsurface flaws of the Acceptance Standards.Copyright © 2007 by ASME